Machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery use linkage systems to accomplish a variety of tasks. These linkage systems often include hydraulic cylinders. Problems can be encountered in the operation of a hydraulic cylinder if a piston within the hydraulic cylinder impacts against an end structure of the hydraulic cylinder. Such impacts can cause undesirable noise, and damage to the cylinder or other components of the linkage system.
Limiting the motion of an implement (i.e., snubbing) has been utilized to limit damage and noise associated with such implement operation. Limiting may have two steps: (1) determining when to limit motion and (2) limiting the motion of the implement. In the past limiting has been performed to stop the cylinders before cylinder end-of-travel and/or to stop the linkage before it reaches a hard stop (e.g., before a bucket implement contacts the linkage). Therefore, determining when to limit may involve determining cylinder position, linkage position, or other positional factors. Further, limiting has been accomplished by slowing down a hydraulic pump and/or by closing a valve through which the pressurized hydraulic fluid flows to the implement cylinders.
A variety of systems (e.g., sensors and electro-hydraulic devices) have been used to effect the limiting of the implement motion when the implement nears a stop point (e.g., end-of-travel of the linkage and/or cylinder). These systems can include cylinder position sensors that are in communication with electronically actuated hydraulic valves. For example, U.S. Pat. No. 5,701,793 (the '793 patent) issued to Gardner et al. on Dec. 30, 1997, describes an apparatus for controllably moving a work implement. A joystick position sensor senses the position of the control joystick, while a implement cylinder detecting means provide information to a controller. This information is processed and a signal sent to a valve for driving a hydraulic cylinder (i.e., the cylinder control means) to control flow into and out of the cylinder.
Although the fluid cylinder system of the '793 patent may provide position and velocity information for controlling electronically actuated hydraulic valves to mitigate impacts (e.g., noise and damage to cylinders), the fluid cylinder system operates at all times (i.e., no determination of when limiting should be turned off), which may cause operator frustration and a loss of productivity because of a slowing implement as the implement nears a stop point.
The present disclosure is directed at overcoming one or more of the problems or disadvantages in the prior art control systems.